The present invention is a process for the preparation of omega-alkenylchlorosilanes. The process comprises reacting a mixture comprising an alpha,omega-diene (.alpha.,.OMEGA.-diene) and an organohydrosilane in the presence of a supported platinum catalyst to form an .OMEGA.-alkenylchlorosilane, where the mole ratio of the .alpha.,.OMEGA.-diene to the organohydrosilane is within a range of about 6:1 to 50:1. A preferred process is run as a continuous process employing a fixed-bed of silica gel supported platinum catalyst and excess .alpha.,.OMEGA.-diene is recovered and recycled to the process.
Addition reactions between compounds containing silicon-hydrogen linkages and compounds containing aliphatic unsaturation, typically referred to as hydrosilylation or hydrosilation reactions, are well known in the art and provide a means of forming a wide variety of products. These addition reactions can be employed to form monomeric materials or polymeric materials which are useful, respectively, as intermediates in the preparation of more complicated products and which are useful as coating materials, elastomers, and insulating materials.
Of particular importance to the coatings industry is the use of the hydrosilylation reaction to react an organohalosilane containing at least one hydrogen with a .alpha.,.OMEGA.-dienes to form organohalosilanes having silicon-bonded groups containing olefinic unsaturation. Typically during the hydrosilyation reaction some isomerization of the diene occurs resulting in migration of the unsaturated bond from a terminal to an internal position in the desired silicon-bonded group. Products having such internal unsaturation exhibit low reactivity with respect to further hydrosilylation to produce surface coatings, elastomers, and other products, and thus represent an undesirable component of the reaction product.
Unexpectedly, the present inventors have discovered that migration of the unsaturated bond from a terminal to an internal position in the desired silicon-bonded group can be reduced in the presence of a supported platinum catalyst by controlling the mole ratio of the .alpha.,.OMEGA.-diene to organohydrosilane within a range of about 6:1 to 50:1. The low levels of unsaturated bond migration in the described process, allows the process to be run as a continuous process with recovery and recycling of excess .alpha.,.OMEGA.-diene. At mole ratios of .alpha.,.OMEGA.-diene to organohydrosilane below about 6:1, unsaturation bond migration in the .alpha.,.OMEGA.-diene makes recycling of the .alpha.,.OMEGA.-diene inefficient because of incorporation of an excessive accumulation of diene having an internal unsaturated bond in the alkenylchlorosilane product.
Therefore, an objective of the present invention is to provide a process where there is a reduction in the migration of terminal unsaturated bonds to an internal position within a diene. A further objective of the present invention is to provide a process where excess diene employed in the process can be recovered and recycled to the process while maintaining a high levels of the desired .OMEGA.-alkenylchlorosilane product.
The use of a platinum complex to catalyze the reaction between a compound containing aliphatic unsaturation and a compound containing a silicon-hydrogen bond is well known and has been described, for example, in British patent No. 1,104,206, Pub. Feb. 21, 1968, and by Ashby in U.S. Pat. No. 3,159,662, issued Dec. 1, 1964.
The use of a supported platinum catalyst to catalyze the reaction between a compound containing aliphatic unsaturation and a compound containing a silicon-hydrogen bond has also been described. Wagner, U.S. Pat. No. 2,632,013, issued Mar. 17, 1953, describes a process for reacting an unsaturated hydrocarbon with any compound containing one or more silicon-hydrogen bonds in its molecule. Wagner teaches that the hydrocarbon may have one or more unsaturated bonds. Wagner further teaches that the process can be facilitated by catalysts such as platinum metals, platinum black, platinized silica gel, and platinized asbestos. In the only example of the reactivity of a diene provided by Wagner, it is reported that butadiene reacts with trichlorosilane to produce the two cyclic compounds beta-cyclohexenylethyltrichlorosilane and betatrichlorosilylethylcyclohexyltrichlorosilane. The mole ratio of reactants is not provided.
Wagner, U.S. Pat. No. 2,637,738, issued May 5, 1953, describes a platinum supported on finely-divided charcoal that selectively promotes the 1,2-addition of the siliconhydrogen bond across a pair of aliphatic carbon atoms linked by multiple bonds. In this patent, Wagner provides an example where two moles of butadiene is reacted with two moles of trichlorosilane in the presence of the platinum on charcoal catalyst. The major products of this reaction were reported to be butenyl trichlorosilane i.e. (CH.sub.3 CH.dbd.CH.sub.2 SiCl.sub.3) and bis(trichlorosilyl) butane i.e. CH.sub.3 CH(SiCl.sub.3)CH.sub.2 CH.sub.2 SiCl.sub.3.
Wagner, U.S. Pat. No. 2,851,473, issued Sept. 9, 1958, describes a platinum deposited on the gamma allotrope of alumina as a catalyst for the reaction between compounds containing silicon-hydrogen linkages and compounds containing aliphatic unsaturation. No examples or guidance is given as to the use of the platinum/alumina catalyst with dienes.
British patent No. 1,526,324, Pub. Sep. 27, 1978, describes a group of hydrosilylation catalysts formed by reacting an inorganic solid containing surface hydroxyl groups and aminoorganosiloxy groups with certain platinum compounds.
The type catalysts reported in this patent are representative of the preferred type catalysts in the present process and incorporated by reference herein. However, British patent No. 1,526,324 provides no examples or guidance as to the use of the described platinum catalysts with dienes.
Based upon the cited art, surprisingly, the inventors have found that in a supported platinum catalyzed process for reacting an .alpha.,.OMEGA.-diene with a organohydrosilane, reduction of migration of the terminal unsaturated bonds into the internal of the diene can be reduced by running the process where the mole ratio of the .alpha.,.OMEGA.-diene to organohydrosilane is within a range of about 6:1 to 50:1. This allows for higher yields of the desired .OMEGA.-alkenylchlorosilanes and allows for excess .alpha.,.OMEGA.-diene present in the process to be recovered and reused in the process while maintaining acceptable yields of the desired .OMEGA.-alkenylchlorosilanes.